Non-woven fiber mats are utilized in numerous applications in the construction industries. Examples include fiber mat-faced gypsum board which is used as a structural support and insulating layer; insulating material for buildings, pipes, and machinery; sound insulation material; filters; backing material for roofing products; and, fire resistant backing sheets for materials such as doors, carpets and fabrics.
Non-woven fiber mats, including the mat of the present invention, are typically manufactured by a process known as the "wet" process. This process is well known in the art, and is typified by the disclosure in U.S. Pat. No. 4,129,674.
A typical wet process may be briefly summarized as follows: fibers of predetermined diameter and length are dispersed in an aqueous slurry through a combination of mechanical agitation and chemical dispersants. A continuous fine mesh conveyor, known in the industry as a forming wire, passes through the slurry and is thereby coated with an even, continuous layer of fibers. The fibers are randomly deposited on the wire, forming a non-woven web or membrane. Most of the water passes through the wire. Excess water is removed from the mat by conventional methods, typically vacuums. The membrane is transferred to a second screen conveyer for conveyance through a section of the processing line where it is saturated with a chemical binder. The binder-saturated membrane is then passed through an oven, which sets the binder and evaporates most of the remaining water. This results in the formation a continuous dry mat. The mat is then wound upon a spool for further processing. There are, of course, many modifications to this typical procedure.
Both organic and inorganic fibers are commonly used in fiber mats. Organic fibers such as those made from cellulosics, acrylic, nylon, polyester, and polypropylene are typical. Inorganic fibers such as glass and mineral wool are also used. Glass fibers consist primarily of oxides of silicon, with other mineral oxides present at relatively lower percentages. Mineral wool fibers are typically manufactured from various waste slags such as copper refinery slag, and are therefore very economical to use. They consist of oxides of silicon, aluminum, calcium, and magnesium, and other mineral oxides.
Fibers of varying sizes may be blended together to form the mat. By varying the length and diameter of the fibers the structural properties of the finished product may be altered. For example, fiber with larger dimensions would tend to give the finished mat an abrasive hand or feel.
Fiber mats which utilize a blend of fibers of varying sizes are known in the art. For example, in U.S. Pat. No. 4,637,951 to Gill et al., a fiber mat that uses a blend of "base" fibers and "microfibers" is disclosed. Both are monofilament glass fibers, but the microfibers are smaller in both length and diameter than the base fibers. The resulting mat is said to be more porous than mats produced by previously known methods, and is thus better suited for use as a substrate for subsequently applied coatings such as a vinyl flooring. Similarly, U.S. Pat. No. 4,129,674 to Hannes et al., discloses a wet process fiber mat which utilizes two different sizes of glass fibers. The Hannes mat is formed by combining monofilament glass fibers with elongated glass fiber bundles. The fiber bundles reinforce the mat and improve tear resistance. The mat is suitable for use in the manufacture of roofing materials.
It is also known that mineral wool may be partially or wholly substituted for glass wool in a blended mat. Fiber mats containing up to twenty-five percent mineral wool and seventy-five percent glass wool are described in an article written by Koenig, and entitled "Processed Mineral Fiber in Mats and Papers," (1984 Nonwovens, pg. 133). And U.S. Pat. No. 4,532,006 to Winters et al., discloses a wet process fiber mat wherein the percentage of the mineral wool fibers and glass fibers may be varied up to 100 percent of the other.
Non-woven fiber mats may be utilized as fire resistant backing sheets for materials such as doors, carpets or vinyl fabrics. The relative degree of fire resistance provided by fiber mats depends upon numerous factors, including the size and composition of the fibers, and the composition of the binder. However, these factors also contribute to the functional properties of the mat. Thus, in developing a fire resistant mat the desired functional properties must be considered in addition to the degree of fire resistance.
Moreover, compliance with various fire resistance testing methods is an important consideration in developing such fire resistant mats because many regulatory agencies and building codes rely on these tests in determining the acceptance of building materials used in various applications. Insurance rates may also be affected by compliance with fire resistance testing methods. One of the most widely accepted classifications for fire resistance is found in the National Fire Protection Association (NFPA) Life Safety Code 101. This code scores fire resistance of materials according to a flame spread index (FSI), and classifies flame resistance from Class A through Class E. Materials obtaining a Class A rating are the most fire resistant. Specific procedures for testing the fire resistance of materials are found in the American Society for Testing and Materials (A.S.T.M.) Standard Test Method for Surface Burning Characteristics of Building Materials, A.S.T.M. E 84-87a. Essentially the same test is also described by other schemes, such as NFPA 255, and American National Standards Institute (ANSI) 2.5.
In a non-woven fiber mat that is used as a fire resistant backing it is desirable to obtain the optimum level of fire resistance without sacrificing the functional properties of the mat. One of the primary objectives of the present invention is to provide a non-woven fiber mat which utilizes a blend of mineral wool and glass wool fibers bonded together with a fire resistant binder. The resulting mat has improved fire resistant qualities and optimal functional properties.